Building AppImageKit failing

I am definitely a newby.
I am trying to duplicate the sigrok procedure that they use to make an appimage of pulseview.
I have downloaded the AppImageKit to the root of my user directory.
I have installed and configured the Docker Engine; It passes their demo task verification test.
I have built the target application (pulseview), but I cannot do the steps to complete the process until I successfully build the AppImageKit.

When I execute the build.sh script found in the AppImageKit/ci directory. It spends a significant time downloading stuff, then gets to the point where it should build, and fails, complaining about CMakeLists.txt being missing, among other things.
I have no idea where to go from here.
It would not surprise me if I am missing something, but I am lost here.